An alignment of an image capturing lens to be mounted in a camera module for a portable device or a mobile device needs to be carried out in a short period of time in view of productivity of the image capturing lens. It has been conventionally preferred that conditions for completing an alignment in the alignment be clear. In recent years, portable devices are provided in various models. As such, it is expected that a lens aligning device which carries out an alignment of an image capturing lens included in a portable device be highly versatile. Further, in a case of a wafer-level lens, development of which has been popular in recent years, it is expected that (relative) decentering generated between) (i) lenses included in one of a plurality of lens arrays and (ii) lenses included in the other of the plurality of lens arrays be corrected by the alignment when the plurality of lens arrays are combined with each other.
Note that the term “decentering” denotes displacement in which an optical axis of a lens is deviated from its proper, ideal position. Examples of the decentering encompass (i) a phenomenon (hereinafter referred to as “parallel decentering”) in which the optical axis of the lens is shifted in parallel from the ideal position, (ii) a phenomenon (hereinafter referred to as “inclination decentering”) in which the optical axis of the lens is inclined with respect to the ideal position, and (iii) a combination of these phenomena. The decentering occurs, for example, (i) between both surfaces (front surface and back surface) of a lens or (ii) between a lens and another lens.
The wafer-level lens is an image capturing lens manufactured by carrying out a step in which (i) a plurality of lens arrays, each of which lens arrays includes a wafer and a plurality of lenses, are combined with each other and (ii) a product thus obtained by combining the plurality of lens arrays with each other is divided by each combination of lenses included in the respective plurality of lens arrays. The step is also called a wafer-level lens process.
Patent Literature 1 discloses a lens aligning device which (i) calculates, on the basis of an MTF (modulation transfer function) of an image capturing lens including lens to be subject to an alignment, a defocus characteristic of the image capturing lens, (ii) calculates an inclination of an image surface on the basis of the defocus characteristic, and (iii) calculates, on the basis of the inclination of the image surface, an alignment amount of the lens to be subject to the alignment. Note that the alignment amount of the lens means a direction and a distance of movement of the lens that is generated to move while a corresponding alignment is being carried out.
Note that “MTF” means an index indicating a change in contrast of an image formed on an image surface, which change is generated as the image surface is moved in an optical axis direction. The larger the MTF, the higher resolution power can be determined to be exerted on the formation of the image on the image surface.
Patent Literature 2 discloses a lens unit aligning device which carries out an alignment so that a decentering amount of a combined lens (lens unit to be examined), constituted by a plurality of lenses, is not higher than a predetermined value. Note that the decentering amount of a lens means a direction and a distance which indicate decentering of the lens.
Specifically, in the lens unit aligning device disclosed in Patent Literature 2, light emitted from a point source of light is converted into a parallel light flux by means of a first collimating lens. Then, the parallel light flux is caused to enter the combined lens. A decentering amount of the combined lens is calculated from light rays, which are obtained by converting light emitted from the combined lens into a parallel light flux by means of a second collimating lens. A lens for adjustment is moved on the basis of the decentering amount thus calculated. Thus, the alignment is carried out.
Patent Literature 3 and 4 each disclose a method for manufacturing an image capturing lens through the wafer-level lens process.